Will hypoxia and ocean acidification alter biofilms and hence disrupt their role as a signpost for marine larval settlement?

Hypoxia and ocean acidification are amongst the major environmental threats to many marine populations and ecosystems worldwide. Current evidence suggests that the number and areas of hypoxia zones mapped with human footprints have doubled every ten years since 1960, and the problem has been predicted to further exacerbate due to global warming. At the same time, about one third of anthropogenic CO2 has been absorbed by the oceans, resulting in ocean acidification. The average surface pH has already dropped by 0.1 unit since the early 1900s, and a further drop of up to 0.5 unit has been predicted by 2100.

Microbial communities play a pivotal role in regulating the structure and function of ecosystems. In the marine environment, microbial communities of biofilms also serve as a signpost to guide the larval settlement of many benthic invertebrate species. Ample evidence has indicated that microbial communities are prone to environmental changes. However, it is not known whether and to what extent changes in microbial communities in response to ocean acidification and its interaction with hypoxia may alter larval settlement patterns and subsequently, the community structure of benthic invertebrates.

Using marine invertebrates across three phyla as models (the gastropod Crepidula onyx, the barnacle Balanus amphitrite and the serpulid polychaete Hydroides elegans), we propose a systematic study to test the hypothesis that hypoxia and ocean acidification can individually and interactively affect bacterial biofilm composition and the subsequent larval settlement patterns. Experiments will first be carried out to investigate the individual effects of hypoxia and ocean acidification and later their interactive effects on the biofilm bacterial composition, using high-throughput pyrosequencing techniques. Settlement assays will be further carried out to test the hypothesis that alterations in biofilm bacterial composition due to hypoxia and ocean acidification will affect the larval settlement pattern of the model species.

Results of this novel study will not only shed light on the effects of these two major environmental stressors on marine microbial community, but also for the first time, provide important and necessary scientific information that will enable us to evaluate and predict the ecological consequences and environmental risks of hypoxia and ocean acidification on marine benthic communities in the face of climate change.